The invention relates to a hoisting mechanism comprising a rotatable reel and hoisting cables to be wound onto the reel, the hoisting cables running substantially parallel to one another, and a guide plate having feed-through apertures for the hoisting cables, with at most one hoisting cable running through each feed-through aperture.
Such a hoisting mechanism is known from practice and is used for hoisting heavy loads. These loads are so heavy that it is necessary to use several parallel running hoisting cables. In practice the number of parallel running hoisting cables may be approximately 50. These hoisting cables are fed through the guide plate after which they converge in a so-called xe2x80x9cstrand jackxe2x80x9d to which the load to be hoisted is coupled.
A problem of this known hoisting mechanism is that it is not possible or hardly possible to unwind the hoisting cables from the reel. One of the reasons is that the hoisting cables tangle up. Furthermore, the hoisting cables are not suitable for compressive strain. In practice this means that the known hoisting mechanism only allows the hoisting cables to be wound onto the reel and after the hoisting mechanism has been used in this manner for hoisting a load, the wound up hoisting cables are turned into scrap.
The problem of the known hoisting mechanism not allowing the unwinding of the reel leads to yet another problem, which occurs if the known hoisting mechanism is being used at several places for hoisting a particularly heavy load. In that case it may be necessary to reposition the load to be hoisted, for which purpose one or more of the hoisting mechanisms may have to undergo an adjustment in height. For reasons explained above, this is not possible with the known hoisting mechanism, so that such exceptionally heavy loads cannot be hoisted with the known hoisting mechanism.
It is the object of the invention to remove the above-mentioned problems and to achieve further advantages, which will be explained below.
The hoisting mechanism according to the invention is thus characterized in that for each hoisting cable a guide member is provided between the rotatable reel and the guide plate, which guide member is embodied as a spiral spring whose coils abut to one another and whose inside diameter is dimensioned such that the hoisting cable fed through the spiral spring is able to move in the feed direction.
Surprisingly it has been shown that the problems of the known hoisting mechanism are solved by using spiral springs for guiding the hoisting cables. This is all the more surprising since a perhaps obvious solution in the form of a tube does not solve the problems. It is therefore essential for the invention that the guide member takes the form of a spiral spring.
Desirably, the coils of the spiral spring abut so closely that when the hoisting cables come under stress, the mutual contact between said coils is maintained.
Because the guide member is embodied as spiral spring, even a tightly-wound one as just now mentioned, it is able to allow the spiral springs to assume a position such that when the hoisting cables are under xe2x80x9cheavyxe2x80x9d strain, the forces over the individual hoisting cables are distributed optimally.
It is further desirable for the inside diameter of the spiral spring to be dimensioned such that some lateral movement of the hoisting cable in the spiral spring is possible. For example, if the hoisting cables have an outside diameter of 18 mm, an inside diameter of 23 mm will suffice very well for the spiral spring, especially with a view to allowing enough free space for movement in the portion of the spiral spring where it bends.
It is further advantageous for a comb member to be provided near the reel for the individual guidance of each hoisting cable from the reel to the guide member of that hoisting cable. This effectively aids in preventing the hoisting cables from tangling up.